The international climate change regime and general principles of law

Abstract The Climate Change Advisory Opinion (AO) by the International Court of Justice (ICJ) demonstrates the growing prominence of general principles of law in international law. The Climate Change AO was handed down at the end of the International Law Commission's project on general principles of law with the adoption of its Draft Conclusions. In the Climate Change AO, the ICJ accords general principles of law particular importance in environmental protection. This article documents how States identified general principles of law as the bedrock of the international climate change regime, and how the ICJ employed a systematic approach to ‘thicken’ climate change law, both in terms of normative content, obligations and consequences of breach. It then examines the general principles of law affirmed by the ICJ, in particular, the principles of common but differentiated responsibilities and intergenerational equity, both extracted from the broader general principle of equity. These principles guide the interpretation of ‘how far’ or ‘how much’, operating as balancing tools in relation to other obligations. The broader significance of this development lies in the ICJ's growing recognition of general principles of law as a means of supporting and structuring its legal reasoning. The article further argues that the normative development of these principles has been reinforced by reports of the Intergovernmental Panel on Climate Change (IPCC), and that Article 38(1)(c) of the ICJ Statute provides a broader gateway for taking account of normative contributions by actors such as the IPCC. The identification of customary law and peremptory norms ( jus cogens ) is more narrowly defined than general principles of law. The article concludes by examining the IPCC's role in underpinning the normative character of certain general principles of law, building on the interaction of law and science, and suggests that strengthening these principles may facilitate their more robust incorporation into future treaty‐design mechanisms.